The host's message listener trusted the compile-time WorkerToHost shape on
traffic from a peer that runs model code: postMessage(null) threw in the
listener and crashed the host process; forged log/done messages bypassed
maxLogBytes/maxValueBytes (the worker-side LogBuffer and prepareValue cap
only honest flows); and the error-reply renegotiation re-echoed a forged
non-cloneable call id, throwing outside any catch.
Every inbound message now passes a runtime shape gate that validates and
REBUILDS it field by field (junk drops without a throw; call ids must be
numbers, so replies are always clone-plain; forged extra fields never ride
along). One host-side ledger bounds everything landing in logs — honest
port entries, forged ones, and stray pipe bytes — at the single documented
maxLogBytes, with the shared in-band truncation marker emitted host-side
when the ledger trips first; the completion value is re-capped host-side
through the same prepareValue (with exactly the truncation suffix as slack
so honest worker-capped values pass unchanged), and done error text is
bounded. Also folds the stray-capture budget into that shared ledger
(round-1 finding B: it was a second maxLogBytes on top of the documented
shared cap).
Tianyi Cui
aa2a7f9a8a